Method for improving the ductility of high-carbon-steel tempered wire



Feb. 5, 1946. H, ,1 ELMENDQRF 2,394,434

'METHOD FOR IMPROVING THE DUCTILITY 0F -cARBoN-STEEL TEMPERED WIRE Filed Dec. 18, 1943 HIGH ' wia/p' .Ja way/265g Awa/5d "fa/wahr:

MKM /Jf ifa/weg 'ultimate Patented Feb. 5, 1946 METHOD FOR IMPROVING THE DUCTILITY F HIGH-CARBON-STEEL .TElVllERED WIRE Harold J. Exmenao'rf,

Cleveland, Ohio, asslgnor to The American Steel andWire Company of New Jersey, a corporation of New Jersey Application December 1s, 4194.3, serial No. 514,845

2 claims. (ci. '14s- 2155) This invention is for the purpose of increasing the ductility of high-carbon-steel tempered wire without materially changing its .tensile strength and elastic limit.

It is to be understood that high-carbon-steel tempered wire is high-carbon-steel wire that has been continuously heat treated, the treatment consisting of austenitizing, quenching and tem'- pering in straight line operation, the heat treating cycles being so chosen that the heat treated wire meets the desired specifications. is usually thereafter coiled in bundles with a suicient radius tovkeep the wire free from cold work strain due to its coiling. The wire is rendered substantially martensitic by suitably quenching the same and its structurefis converted to substantially tempered martensite by any conventional tempering treatment, this providing the wire with the high tensile strength and elastic limit required of high-carbon-steel tempered wire.

However, sometimes the wire does not have adequate ductility, and it is in such instances that the present invention comes into play.

According to the present invention, the highcarbon-steel tempered wire, free from cold work strain, is-maintained at temperatures of from about 300 to 600 F. for a time controlled to increase its ductility without materially changing its tensile strength and elastic limit. The exact Y time of the treatment may be easily determined by tests although from about one to twelve hours is usually considered preferable. Furthermore, it will be found that for diierent compositions of A high-carbon steel, different temperatures, within the range, provide the maximum increase in ductility, as contrasted to the thought that the maximum temperature will always provide the maximum ductility. The exact temperature best suited for a particular steel composition may also -be easily' determined bytests, it being deemed best that the wire be maintained within the denned range, at about the temperature predetermined by testas providing the maximum increase in ductility without materially changing the tensile strength and elastic limit for high-carbonsteel tempered wire oi about the same chemical composition.

In the accompanying drawing:

Figure 1 graphically shows the effects produced by the invention on the proportional limit and tensile strength of tive different compositions oi high-carbon-steel tempered wire; andv Figure 2 shows the effects on the ductility as indicated by the per cent reduction oi area.

The various wires identied on the illustrated graphs involve the lollowing compositions:

The Wire- In further explanation of the graphs, the points represented at 0 F. on both graphs are values obtained by testing the various specimens immediatelyv after their tempering, and the various points represented at 90 F. in Figure 1 are values after the specimens had been held for 90 hours at room temperature, while the points at F. in Figure 2 also represent values after the specimens were held for hours at room temperature. Other than noted, the treatment time was in al1 instances one hour.

It will be seen that in all instances there is an increase in the ductility at temperatures between 300 and 600 F. without any material change in the elastic limit or tensile strength. Due to the time requirement the present invention is probably best carried out by appropriate baking ovens with the wire in its usual coiled bundle form.

The present invention is to be distinguished from the practice of bluing coiled springs containing cold work strainfresulting from the smallradius coiling required to produce Ythe spring shapes. In this process steel containing cold workstrain and results in raising the elastic limit of the metal. In the case of the present invention, the baking treatment is4 not appliedthe steel containing any material cold work strain at all and it does not affect the elastic limit materially.

I claim: y

1. Maintaining high-carbon-steel tempered wire free from cold work strain at temperatures of from about 300 to 600 F. for a time controlled to increase its ductility without materially changing its tensile strength and elastic limi 2. Maintaining high-carbon-steel tempered wire free from cold work strain at temperatures of from about 300 to 600 F.'for a time controlled to increase its ductility without materially changing its tensile strength and elastic limit, the wire being maintained at about the temperature within said range predetermined by test as providing the maximum increase in ductility without materially changinl the tensile strength and elastic limit for high-carbon-steel tempered wire o! about the same chemical composition.

HAROLD J. ELMENDORF.

batch heating methods inl the bluing is applied what might be termed 

